What factors influence population numbers. Resources are limited

What is a population? What can happen to the environment and the organisms if the population grows too fast? You will learn the answers to these questions and other facts related to populations and their growth in this lesson.


Example of an American Family.
African-American Family

A population is any group of organisms of the same species, living in and depending on, a specific area for all of its needs. Did you know that in the late 1800s the average American Family consisted of five family members? By the early 1900s the average family in the U.S.

had dropped to four family members. By the mid to late 1900s the average American family had dropped to three and then closer to two family members. What was contributing to the changes in family and population in the U.S? Did you know that in China the government actually adopted a policy that limits most couples to only have one child? Both the U.

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S. and Chinese occurrences are examples of limits that were being placed on a population, one was government enforced and the other was self inflicted. Why would an organism want to restrict population growth? Are there limits placed on the populations of other organisms that occur naturally? In this lesson, we’ll take a look at the answers to population growth issues.

What Is a Limiting Factor?

No population of organisms can grow uncontrollably. Limiting factors, are anything that places restrictions on how large a population can grow. The example above demonstrates a trend that occurred in American families. Nuclear families in America have shrunk over time. Why? What problems do large families face? Could it be the cost of food? What about the cost of housing? All organisms have a ‘cost’ associated with obtaining their needs. Humans have to spend money on their needs, while animals spend different resources, like time and energy, obtaining their needs. These are all ‘cost.

‘ These costs often act as limiting factors.If a family does not have the means to obtain a substantial amount of money, having a large family can become a disadvantage. If the food an animal eats starts to become scarce, having many offspring can become a disadvantage. This is how limiting factors influence population numbers. Resources are limited in every environment. Food, water, shelter, soil and hunting space are all examples of resources. When a population grows, these things become even more limited.

Could this be why China has taken such drastic steps to control its human population? How will the government afford healthcare, work on roads or facilitate efficient transportation if one of the most populous countries has even more inhabitants?

Carrying Capacity

What will happen initially to any population if they have all of the food, water, air, and living space (limiting factors) they need for the time being? Well, the population will grow! However, as a population grows, resource, such as jobs, food, water, shelter, soil, and hunting space, can become depleted. No environment has an unlimited amount of resources. As a population gets larger, the organisms in the population start to compete for the limited resources. Some organisms win the fight, but others lose. Think about the things that can happen to a population when they start to run out of living space and become over-crowed. Disease is one of the limiting factors that grows as a population reaches its environments’ upper limit for that population, or carrying capacity. What happens to the population as more of its members carry disease and lose the competition for resources? As an environment reaches its carrying capacity, some of them will die, and the population will decrease.

In the 1300s, the bubonic plague effected the human population in Europe very much like we have discussed. The population became very large for the environment. As the human population increased, space decreased, and they began living in close quarters. As humans began to live closer, so did the organisms that depended on them, namely rats. As the rats continued to interact with the humans, a disease they carried (the bubonic plague) began to infect the humans. As more humans died, more humans came in contact with the diseased bodies, and they died as well. The human population in Europe plummeted drastically; it’s believed that anywhere from 30-60% of Europeans died.

Eventually the population rebounded.

Flows Like a River

As you can see from the explanations above, population is a not a static thing. It does not stay constant. Environmental changes and limiting factors keep the population from growing out of control, but it does not keep the population at a constant number.

The population of any organism can grow sharply, perhaps because of the introduction of a new food source. The population will then eventually decrease because of other limiting factors. The population of a wild animal or plant can also go through a large decrease because of loss of habitat to construction or other human activity. As long as the population of an organism is not driven to extinction, it it will continue to rise, fall and fluctuate.

Governments keep a close eye on its population numbers because they want to make sure their inhabitants can be healthy, safe, and productive citizens. Unchecked rises in population numbers can effect these goals.

Lesson Summary

All population numbers are controlled by limiting factors.

Limiting factors are environmental factors that keep a population’s numbers from growing out of control. Some examples of limiting factors are food, water, living space, and disease. The maximum number of any one organism that an environment can support is the carrying capacity. Population numbers are not static, they go up and down based on limiting factors and other environmental occurrences.


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